In the Next Generation Network (NGN), there are many Media Gateways (MGs) based on Media Gateway Control Protocol (MGCP) or H248 protocol (another Media Gateway Control Protocol, i.e., MeGaCo); these numerous MGs are distributed in enterprises or residences widely, and are featured with covering a wide range, having a great quantity, and being based on dynamic IPs. However, because there being no security authentication mechanism on the application layer of MGCP protocol in the current NGN, the MGs using MGCP protocol are poor in security; though H248 protocol has security authentication mechanism on the application layer, i.e., a security header can be added into each transaction request message of H248 protocol, and the security authentication result can be returned in the transaction response message, but the security authentication mechanism requires exchanging a large amount of H248 messages between MGC and MG, resulting in increasing about 40% time for processing of encoding and decoding H248 messages; thus a security authentication solution provided by conventional H248 protocol severely degrades efficiency of the network system and its feasibility in actual application is poor. Therefore, the problems of system security in the NGN, such as forging MG or attacking to MGC are yet not solved.